The present study was carried out with the primary objectives to assess intercultivar (intra – specific) variation for salt tolerance in cotton at different stages of plant life cycle Thus eighty local and exotic cultivars / lines were screened at three growth stages, e g , germination, seedling and adult Germination experiment was conducted in Petri dishes under greenhouse conditions The NaCl concentration applied were 0, 70, and 140 mol m 3 It was possible to categorize all the cultivars / lines into four different groups on the basis of their difference in salt tolerance Twenty six cultivars were placed in tolerant group having germination range (average of 70 and 140 mol m 3 NaCl treatments) from 50 00 to 64 18% The moderately tolerant group had a maximum number (36) of cultivars / lines which had germination range from 40 00 to 49 99%, whereas the moderately sensitive group displayed the germination range from 31 00 to 39 99% The sensitive group included only three cultivars, MNH – 147, Culture – 604 – 4 and B – 1580 (ne)
The seedling experiment was conducted in soil + sand (1:1) culture, salinised with 0 or 140 mol m 3 NaCl, using the same number of lines as in the germination experiment The cultivars / lines were classified into three groups on the basis of their performance in percent shoot dry weight In the tolerant group, having more than 70 percent dry weight of control, the cultivar MNH – 156 had the maximum value for shoot dry weight followed by B – 557 and Culture 728 – 4 The moderately tolerant group ranged from 50 0 to 70 0 percent The sensitive group had six cultivars of which B 1580 (ne) had the lowest shoot dry weight followed by Culture 604 4
To assess whether the lines, tolerant at initial growth stages, maintain their salt tolerance as adult, three tolerant cultivars (B 557, Culture 728 4, MNH 156) and three sensitive cultivars (B 1580 (ne), Culture 604 4, MNH 147), selected on the basis of their performance at germination and seedling stages, were grown in salinized soil under naturally lit greenhouse conditions Four treatments of NaCl, i e , control (ECe=1 6 dSm 1), 70, 140 and 210 mol m 3 were applied after ten days of initial growth and the experiment continued until maturity Seed cotton yield and its components were adversely affected due to NaCl in all the six cultivars, but the three salt tolerant cultivars produced better seed cotton yield than that of the three salt sensitive cultivars Ginning out turn fibre fineness increased with increasing concentrations of salt, whereas staple length, fibre maturity and fibre strength showed a decreasing trend at higher salt concentrations (140 and 210 mol m 3 NaCl) The salt tolerant lines had lower ginning out turn, but higher staple length, fibre maturity, and fibre strength and than those of the salt sensitive cultivars The salt tolerance and salt sensitive lines did not differ in leaf or root Na+ The salt sensitive cultivars/lines accumulated more C1 in the leaves than all the salt tolerant cultivars/lines at the highest salt level The salt tolerant cultivars/lines had higher concentrations of K+, Ca2+, N and higher K/Na ratios in the leaves than those of the salt sensitive lines at the highest NaCl concentration, whereas no relationship could be drawn between the salt tolerance and tissue P concentration The seed oil content of the salt tolerant cultivars/lines was slightly higher than that of the salt sensitive cultivars/lines The tolerant cultivars, generally, had higher leaf water potential, turgor potential and osmotic potential than those of the salt sensitive lines
Inheritance pattern of salt tolerance of cotton was also studied, using diallel crossing model in which six cultivars/lines, differing in salt tolerance, were crossed in all possible combinations The salt tolerance of 36 crosses, including self s, was assessed in soil salinized with 140 mol m 3 NaCl The genetic components of variation for salt tolerance were estimated for seed cotton yield, boll per plant, monopodia per plant, sympodia per plant, plant height, seed oil content, ginning out turn, staple length, fibre fineness, fibre maturity and fibre strength The results from scaling tests for the adequacy of additive dominance model suggested the failure of only one parameter, ginning out turn, whereas all the other characters were fully adequate or partially adequate for further genetic analysis Seed cotton yield number of bolls per plant, plant height, staple length, fibre fineness, fibre maturity and fibre strength were controlled by additive genes while over dominance was prevalent in monopodia per plant, sympodia per plant and seed oil content characteristics The salt tolerant cultivars/lines being farther from origin contained maximum recessive genes Positive values of correlation coefficients between Wr+Vr and mean parental values for all characters, except for fibre maturity, suggested that recessive genes were mainly responsible for yield, yield components and fibre quality characteristics High narrow sense heritabilities, estimated for seed cotton yield, different yield components and fibre characteristics, indicated that these parameters could be effectively improved through selection in the segregating populations
The ultimate objective of the present study was to assess whether it is possible to improve salt tolerance of cotton using conventional selection and breeding strategy Thus five thousand seeds of F2 variable seed material, obtained from a 6 6 diallel of cotton (Gossypium hirsutum), were screened at the seedling stage after four weeks growth in soil salinized with 210 mol m 3 NaCl It was possible to select only twenty seedlings, using phenotypic vigour as selection criterion The selected and unselected lines were allowed to grow till maturity in non saline medium The selected line was then compared with the unselected line for salt tolerance at varying NaCl concentrations The selected line produced relatively better seed cotton yield but it did not excel significantly the unselected line Relationship between degree of salt tolerance of the two lines and accumulation of different ions in their plant parts were not possible to be drawn from the data presented here
From all the results of the present study, it is possible to conclude that degree of salt tolerance of cotton does not vary with the change in the growth stage Thus selection from the variable material carried out at the initial growth stages gave rise a selection line which was superior to the unselected base population in growth and yield Physiologically, accumulation of C1 , K+, Ca2+, and N in the leaves has a positive relationship with the salt tolerance of cotton Low ginning out turn and high staple length, fibre maturity and fibre strength are associated with the salt tolerance of cotton